jet-hot, pacesetter, and hooker all have a flattened portion on the driver's side. My jet-hot Y hit the floor board at the flattened part and caused false knock--so I cut a big piece of radiator hose lengthwise and put it between the y-pipe and floor. Now there is no knock and no, the hose doesn't melt to the pipe. Very cheap and surprisingly effective fix. Whether the pipe hits is all very characteristic of the engine and how it sits. If your motor mounts are sagging it wouldn't surprise me at all if the pipe cleared better--I put in some new Prothane mounts when I installed headers...this made the engine sit quite upright with the headers tilted forward a bit.
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